Water heater



FIG. 1 is a front and left side perspective view of a water heater showing our new design;

FIG. 2 is a side elevation view thereof, the opposite side being a mirror image of that shown;

FIG. 3 is a front elevational view thereof;

FIG. 4 is a top plan view thereof; and

FIG. 5 is a rear elevation view thereof. 

The ornamental design for a water heater, as shown and described. 